Project: sc090025/R1

Table 2.1: Units used commonly in the pumping industry 
 
Preferred unit 
Legacy units 
Power 
Watt or kilowatt (W or kW) 
Horsepower (HP) 
Flo rate 
Cubic metres (cumecs) or litres per 
second (m
3
/sec or l/sec) 
Cubic feet per second (cusecs) or 
gallons per hour (cubic feet/sec or 
gal/hour) 
Dimensions 
Metres (m) or millimetres (mm) 
Inches or feet (inches or feet) 
Pressure 
Bar gauge or absolute; metres
(barg or bara; m) 
Inches water or mercury
(inches H
2
O or inches Hg) 
Energy 
Joules or kilowatt-hour
(J or kWh)
British Thermal Unit, ergs or calories
(BTU; ergs or cal) 
Time 
Seconds (sec) 
Seconds (sec) 
Force 
Newtons (N) 
Pounds-force; Dyne (lb; Dyn) 
2.2 Carbon usage 
Carbon emissions from power generation can be calculated in a number of ways depending on 
the efficiency of the power transmission system, the method of generation and the ultimate 
energy source. In order to ensure a fair comparison between different pumping schemes and no 
artificial advantages from some areas having access to low-carbon power, we decided to use a 
common and standard figure for carbon emission from power generation.
The Grid Rolling-average Electricity Emissions Conversion Factor (GREECF) between carbon 
emissions and electricity generation is a common measure of the environmental impact of 
power generation used by industry when comparing the cost of their power. In June 2010, the 
conversion factor
(Defra, 2009a)
was 0.537 kg CO
2
e/kWh; this figure was used in the 
calculations in this report.
A number of factors do not impact directly upon carbon emissions resulting from pumping 
station operations. Examples of carbon-intensive items which may be encountered at pumping 
stations include: 
•
building structure modifications; 
•
pipework and changes to associated items; 
•
control systems upgrades;

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4 
•
staff travel to and from the sites. 
Carbon footprints associated with travel are well understood; for example, figures are readily 
available (Defra 2009b,c,d; Department for Transport 2009) for personal transport, small HGVs 
and larger vehicles, and as a result little additional work can be done in this area, other than to 
reduce the number of miles driven for specific tasks. This can produce undesirable 
consequences as the number of maintenance visits to individual sites will be reduced, with 
some of the more remote assets suffering the longest periods between maintenance activities.
This project does not investigate the carbon costs associated with this travel or maintenance 
activities, but focuses only on the pumping operations. 
The inefficiency of pumping stations may be caused by a number of factors which may be 
summarised as follows: 
•
Incorrect selection and/or sizing of the primary pumping system components. 
•
Poor design of the pumping system, including intake and sump, pipework layout, 
discharge. 
•
Control system and station operating philosophy. 
•
Deterioration of pump impellers and associated moving parts. 
•
Deterioration of pump and pipework surfaces in contact with the moving liquid. 
Each of these factors may have a significant effect on the efficiency of the pumping station. 
They may also combine to result in greater inefficiency than the sum total of the individual 
items. For example, a damaged oversized pump and undersized pipework system would 
combine to result in a greater inefficiency of the overall system. 
2.3 Life cycle costs 
It is often thought that fitting oversized pumps does not lead to any loss of performance or 
increased operating costs as an oversized pump will generally tend to operate for less time; 
however, this is not always the case as higher delivery flow rates can increase frictional losses 
in pipelines and hence incur greater operating costs. Further costs may be associated with 
increased power supply requirements and greater requirements for the control systems. 
Flood defence applications (which operate intermittently) tend to have relatively low annual 
power usage compared with water industry systems (which tend to operate continuously all year 
round) so the figures below may require some adjustment; however, Figure 2.1 clearly 
demonstrates that if the most efficient pumps are not selected at the start, an opportunity is 
missed to contribute to sustainable design.